feature request: `#` flag should turn off checksum when formatting descriptors

[apoelstra]

This would avoid the need for hacks like to_string_no_chksum in elements-miniscript, where we wrap descriptors in other stuff and add a new global checksum.

[sanket1729]

concept ACK. Will get to this one this week

[apoelstra]

I beat you to it :) I have an implementation that I will push in the next 10 minutes, once my tests all pass on 1.41.